Geo-thermal AC

[AustinScoobee]

Anybody used Geo-thermal AC system in Central Texas, and if so do you know of any contractors who do it in the area? We are looking into it, but the basic idea that the ground temp is

65deg @ 5ft below grade seems hard to beleive in this region, where 100 der all summer is common. Anyone have any actual use experience with these? G

[dpb]

Not in TX, but SW KS so the answer to (1) and (2) are--I'm sure there is somebody and no, I don't know a contractor near you... :)

But, your supposition that 65F at 5-ft all summer is overly optimisitic is certainly true. However, even if it is as high as 70F, that's a fair cry better than 100+F for an air-air exchanger. To work well, you'll definitely want to be 6-ft or deeper and a well-system would be even better if feasible.

I have actually had a ground-loop system while in E TN, and can attest it cut our utility bills by well over a third as compared to an old, tired, air-air system it replaced. I can strongly recommend WaterFurnace as a manufacturer based on that system and at least at that time they were pretty selective in dealerships. Even there, however, the trench was 6-ft, not 5-ft deep although there they laid a second loop in the same trench about 2-ft above the bottom one. In TX, that may not be a good option.

The Water Furnace people do a thorough job of analyzing the site conditions and do detailed sizing calculations. I've not looked recently, but when I was doing the research before the we did the system in TN, OSU-Stillwater was _the_ research center for geothermal and had a web site full of useful information. I would assume you can also get a good amount from UT as well.

Last thing I'll note--it won't be an inexpensive installation for an existing house owing to the need for the excavation, etc. That can be allayed somewhat if it is new construction by judicious scheduling, but is unavoidable for retrofit. In TN, at the time we did not have access to gas, so the economics were somewhat tilted. I'm near the point of needing a replacement system here and am certainly going to investigate it here even though we have the similar summer climate as you and colder (or at least longer) winters and do have gas.

[Jonny]

Bear in mind the subsurface soil temperature will gradually increase as global warming continues. That includes limestone strata typical in the foothills of the TX hill country. As the area becomes drier, due to lack of rainfall, suspect this will accelerate.